In typical multi-cell wireless communication systems, a Gaussian assumption has been applied to an interference signal in order to perform decoding with lower complexity. Therefore, a conventional wireless communication system has used mainly a QAM-series modulation scheme to render a characteristic of an interference signal closer to a Gaussian distribution as much as possible.
However, since a non-Gaussian channel has a greater channel capacity than a Gaussian channel, the non-Gaussian channel may offer higher decoding performance than the Gaussian channel if a suitable decoding is performed. For this reason, the development of a modulation scheme that allows an interference signal to have a non-Gaussian characteristic has been needed, so that FQAM has been proposed as a modulation scheme.
As shown in FIG. 1, FQAM is a hybrid modulation scheme for combining QAM with FSK, thus having both a higher spectral efficiency of QAM and a characteristic of FSK to form an interference signal in a non-Gaussian distribution.
Meanwhile, for more reliable communication using a plurality of antennas in a wireless communication system, transmit diversity techniques such as a space frequency block code (SFBC) and a space time block code (STBC) have been studied actively. However, since such transmit diversity techniques are induced on the assumption that a channel is unvaried within a frequency or time block, a serious degradation of performance is caused in case the channel is varied in such a block. Particularly, since a single symbol occupies a plurality of subcarriers (or OFDMA symbols) in the above-mentioned FQAM (or TQAM), simply applying the existing transmit diversity technique may invite a serious degradation of performance in a channel-varying environment. Accordingly, required for FQAM (or TQAM) is a transmit diversity technique that does not cause a serious degradation of performance even in a channel-varying environment.